The problems encountered in producing foam-based sheets or pads designed to meet household cleaning needs have been addressed by a variety of products. Polyurethane foam-based sponge products which have been disclosed fall into two general classes, which may be designated as dry and moist. Dry sponge products are disclosed by Strickman et al in U.S. Pat. Nos. 4,271,272 and 4,421,526. These products are formed by reacting isocyanate-capped polypropylene glycol resins with small amounts of water and organic catalysts, followed by stirring powdered detergents and/or abrasives into the foaming resin. Since the molar ratio of water to free isocyanate groups on the resin is generally adjusted to about 0.5 or less, the cured foam which is obtained is dry. This results in additives such as abrasives and detergents being largely deposited in the cell voids, thus reducing the sponge's absorbency. When the sponges are remoistened, the additives must re-emulsify prior to becoming available for application in a cleaning operation.
The preparation of open-celled, hydrophilic or "moist" polyurethane foams by the reaction of specially-formulated prepolymer isocyanate resins with large molar excesses of water without the need for added catalysts or cross-linking agents is disclosed in U.S. Pat. Nos. 3,890,254; 4,137,200 and 4,160,076. These resins permit the introduction of large amounts of solids into the foam matrices via preformed aqueous slurries of solid particles which are subsequently reacted with the prepolymer resin in order to foam it into the desired specialty product. The finished foams are very hydrophilic, or water-absorbent, due to the entrapment of excess water within the cell walls.
U.S. Pat. Nos. 3,833,386; 4,066,394; 4,066,578; 4,309,509; and 3,343,910 describe the incorporation into hydrophilic foams of sinterable ceramic materials, water-softening minerals such as zeolites, flame retardants, odorant-containing waxes and fine abrasives, respectively. In order to produce solids-loaded foams for use as polishing pads, sachets, water-softening sponges, cushions and the like, the weight ratio of aqueous phase to resin must be maintained at a value low enough so that the foam matrix exhibits satisfactory overall integrity. Increasing the weight of additives in foamed products formed by this method necessarily requires the use of higher ratios of water to prepolymer resin, which in turn attenuates the polymeric cellular matrix which is further embrittled by the introduction of the solids. Surfactants which result in a highly reticulated, open-celled matrix also reduce the absolute strength of the foam due to the removal of cell window membranes. Although reticulated, open-celled, hydrophilic polyurethane foams which are highly loaded with particulate abrasvies are desirable due to their optimal cleaning power, when the weight ratio of dispersed abrasives in the aqueous phase to the presently-available prepolymer resins exceeds a certain value, the resultant foams will become friable. These foams are unsuitable for use as cleaning pads and sheets due to their low tensile strength which causes the cured foams to flake or crumble during use.
Thus, it is an object of the present invention to provide cleaning pads or sheets comprising a moist, hydrophilic polyurethane foam which incorporates a large amount of particulate abrasive and which further incorporates effective amounts of detergent surfactants.
It is another object of the present invention to provide resilient cleaning pads or sheets suitable for cleaning a wide variety of surfaces comprising open-celled, highly -reticulated, hydrophilic polyurethane foams of low tensile strength which comprise abrasive particles and detergents integrally incorporated within the cellular matrix of the foam.
Other objects and advantages of the present invention will become apparent from the following description and appended claims.